Try using galvanized deck screws driven with a drill/driver

Thanks for the response. Yeah, i did think about using screws is places, such as near the room perimeter and under cabinets, but I was worried about the "cancellation of warranty" if screws are used. I guess it's like anything else where warranties apply. Any more thoughts folks?

I wonder why they would cancel warranty with screws in the underlayment? I don't get it.

The Armstrong dealer I bought the vinyl from specifically stated and is included with my warranty papers that no screws be used. My guess is that perhaps if the screws work loose, the heads cut the underneath side of the vinyl. That's my best guess but they must have a reason for being so demanding. Don't know if being on the east coast might play into it. At any rate, I might still try that because they don't glue the vinyl down anymore, so it's easier to manipulate.

The problem stems from the fact that you should have also glued the plywood to the floor joists before using the nails.